class_docstr: Test upgrade_opt behavior.
code: def _get_threshold(self):
      # Accuracy threshold
      return 0.8
  
imports: import os
  import pytest
  import unittest
  import parlai.utils.testing
  from parlai.tasks.integration_tests.agents import CandidateTeacher
label_desc: Use image node_id 3 for calling the _AbstractTRATest obj's underlying member method code with example usage: obj._get_threshold() and returns: int